The present invention relates to a method of producing a thin metal sheet or ribbon and, more specifically, to a method of extruding or ejecting a molten metal melt from a rectangularly shaped orifice onto a moving cooling surface adjacent to the orifice so that the melt is rapidly cooled by the cooling surface to provide a thin metal sheet or ribbon, particularly a thin amorphous metal ribbon. The melt extruded from the orifice is spread and rapidly cooled to a thin metal ribbon on the moving surface.
Thin amrphous metal ribbons having a width of more than 100 mm are currently manufactured in Japan. The manufacturing process now employed is based on the process which was pioneered by researchers in Tohoku University and the Research Institute of Electric and Magnetic Alloys(RIMEA) in Sendai, Japan.
Previously, a manufacturing process for thin ribbons formed of amorphous metal which employed a rapid quenching apparatus provided with a cooling roll and a slotted nozzle was demonstrated in an exhibition room in a new RIEMA building to celebrate the completion of the new building on July 8, 1976. The manufacturing process was similar to the process disclosed in U.S. Pat. No. 905,758 issued on Dec. 1, 1908 to E. H. Strange, et al. or U.S. Pat. No. 3,605,863 issued on Sept. 20, 1971 to Derek King. In the demonstration, ribbons of about 8 mm width made of amorphous metal having a clean surface were produced by this manufacturing process. Tohoku Broadcasting Company reported the demonstration in a T.V. program, "Kahoku Sinpo News" which started at 11:20 p.m. on July 8, 1971 and at 7:10 a.m. on July 9, 1971, in the area including Sendai-City.
In the demonstration, the following experimental conditions were used to make the wide amorphous metal ribbons having a thin thickness. The rapid quenching apparatus was equipped with a slotted nozzle having an orifice with a rectangular shape. The gap length between the orifice and the cooling roll surface was about 0.4 mm, the slit width of the slot was about 0.4 mm, each of the lips defining the orifice had a width of about 1 mm measured in the moving direction of the chill surface. About two years later, a similar process for forming an amorphous metal ribbon was desclosed in Narashimhan's Japanese Laid-Open Patent Application 53-53525 on May 16, 1978 in Japan. In both processes, i.e., the demonstrated process at RIEMA and the Narashimhan process, molten metal is extruded from an orifice defined between a back lip, a front lip and side walls through a slot formed in a nozzle in a form of a melt stream onto a rotating roll surface to form a thin amorphous metal ribbon.
However, in the above-mentioned processes, there were drawbacks that the prduced amorphous metal ribbon, especially a ribbon having a thickness of about 25 .mu.m or less might be provided with scratches on the surface or with a rough surface.